The disclosure relates generally to fiber optic cable assemblies suitable for making optical cross connections, in addition to methods for fabricating such assemblies.
Optical fibers are useful in a wide variety of applications, including the telecommunications industry for voice, video, and data transmission. In a telecommunications system that uses optical fibers, there are typically many locations where fiber optic cables (which carry the optical fibers) connect to equipment or other fiber optic cables.
FIG. 1 is a cross-sectional view of an exemplary coated optical fiber 100 that includes a glass core 102, glass cladding 104 surrounding the glass core 102, and a multi-layer polymer coating 110 (including an inner primary coating layer 106 and an outer secondary coating layer 108) surrounding the glass cladding 104. The inner primary coating layer 106 may be configured to act as a shock absorber to minimize attenuation caused by any micro-bending of the coated optical fiber 100. The outer secondary coating layer 108 may be configured to protect the inner primary coating layer 106 against mechanical damage, and to act as a barrier to lateral forces. The outer diameter of the coated optical fiber 100 may be about 200 μm, about 250 μm, or any other suitable value. Optionally, an ink layer (e.g., having a thickness of about 5 μm) may be arranged over the outer secondary coating layer 108 of the coated optical fiber 100 to color the fiber (e.g., as is commonly used in ribbonized fibers), or a coloring agent may be mixed with the coating material that forms the outer secondary coating layer 108. An additional covering (not shown), which may be embodied in a tight buffer layer or a loose tube (also known as a furcation tube or fanout tube), may be applied to the coated optical fiber 100 to provide additional protection and allow for easier handling, wherein the resulting buffered or furcated optical fibers typically have an outer diameter of about 900 μm.
Groups of coated optical fibers (e.g. four, eight, twelve, twenty-four, or more) optical fibers) may be held together using a matrix material or intermittent inter-fiber binders (“spiderwebs”) to form “optical fiber ribbons” or “ribbonized optical fibers” to facilitate packaging within cables. For example, optical fiber ribbons are widely used in cables for high-capacity transmission systems. Some modern cables in large-scale data centers or fiber-to-the-home networks may contain up to 3,456 optical fibers, and cables having even higher optical fiber counts are under development. Optical fibers that form a ribbon are arranged in parallel in a linear (i.e., one-dimensional) array, with each fiber typically having a different color or marking scheme for ease of identification. FIG. 2 provides a cross-sectional view of a multi-fiber ribbon 112, which includes twelve optical fibers 114A-114L and a matrix 116 encapsulating the optical fibers 114A-114L. The optical fibers 114A-114L are substantially aligned with one another in a generally parallel configuration, preferably with an angular deviation of no more than one degree from true parallel at any position. Although twelve optical fibers 114A-114L are shown in the ribbon 112, it is to be appreciated that any suitable number of multiple fibers (but preferably at least four fibers) may be employed to form optical fiber ribbons suitable for a particular use.
Optical communication systems utilizing fiber optic cables are a substantial and fast-growing constituent of communication networks, due to the low signal losses and large transmission bandwidth inherent to optical fibers. Hyperscale data centers have emerged in recent years to support high bandwidth communications.
Hyperscale datacenters have been converging into leaf-spine architecture with low oversubscription (wherein oversubscription refers to the practice of connecting multiple devices to the same switch port to optimize switch port utilization). Low oversubscription is critical to support diverse applications such as social media, web searching, cloud services, and artificial intelligence/machine leaning/deep learning.
Leaf-spine network architecture is a two-layer network topology that is useful for datacenters that experience more east-west network traffic than north-south traffic. Leaf-spine networks utilize a leaf layer and a spine layer. The spine layer is made up of switches that perform routing, working as the network backbone. The leaf layer involves access switches that connect to endpoints. In leaf-spine architecture, every leaf switch is interconnected with every spine switch, permitting any server to communicate with any other server using no more than one interconnection switch path between any two leaf switches.
FIG. 3 shows an example of a non-blocking leaf-spine switch network 120 in a full mesh configuration, where each leaf switch 124 has a port connected to a port of each spine switch 122. In the particular implementation of FIG. 3, twelve spine switches 122 and twelve leaf switches 124 are provided, with each spine switch 122 and each leaf switch 124 having twelve ports, for a total of one hundred forty-four links that are provided by optical fibers 126. If each link includes a Small Form Pluggable (SFP) duplex fiber transceiver (having a dedicated transmit (TX) fiber and a dedicated receive (RX) fiber), then the number of optical fibers 126 connecting the spine switches 122 and leaf switches 124 would be increased to two hundred eighty-eight.
A base unit of mesh connectivity can be scaled to interconnect a larger number of switches, limited only by the port count of the switches. FIG. 4 shows a large number of spine switches 132 and leaf switches 134 that are organized in groups (e.g., spine switch groups 133A-133D and leaf switch groups 135A-135H, respectively) providing a super-mesh switch network configuration 130, with a multitude of optical fiber jumpers 136 providing full mesh connectivity between all the spine switches 132 and leaf switches 134. In this example, ninety-six leaf switches 134 are connectible to forty-eight spine switches 132 in a full mesh network using thirty-two base units of mesh connectivity, with each base unit having one hundred forty-four links. As will be apparent, any suitable number of switches can be chosen as the base unit in leaf-spine networks providing full mesh connectivity.
In typical practice, spine switches and leaf switches are physically located in different areas of a datacenter building. Structured cabling is essential to fiber management. Traditional straight trunk cables may be used to bring the fibers close to the spine switches, and then subunits are broken out to connect to individual switch ports. FIG. 5 is a schematic diagram showing a conventional leaf-spine switch network 140 having twelve spine switches 142 and twelve leaf switches 144 that are connected in a mesh configuration using optical cabling 145, with each leaf switch 144 having a port connected to a port of each spine switch 142. Starting from the leaf switches 144, multi-fiber subunits 146 are collected into a trunk segment 147 (typically including a jacket 147A) that spans a majority of a distance between the leaf switches 144 and the spine switches 142. Multi-fiber subunits 148 are broken out from an end of the trunk segment 147 closest to the spine switches 142, and thereafter individual fiber segments 149 are broken out separately from each multi-fiber subunit 148 to connect to a port of each respective spine switch 142. FIG. 5 shows that switch panels (e.g., including spine switches 142) for mesh networks remain highly chaotic and unmanageable. Individual optical fibers are actually harder to trace than would be suggested by FIG. 5, since such figure illustrates just one mesh connection unit, whereas in practice a multitude of mesh connection units would be provided in a typical leaf-spine network.
To enhance manageability and traceability of optical fibers in mesh network switch panels, one solution is to insert an optical shuffle box between a trunk cable and spine switch to provide a full mesh cross-connector pattern. An example of such a solution is shown in FIG. 6, which illustrates a leaf-spine switch network 150 that includes a trunk cable 155, an optical shuffle box 160, and jumpers 166A-166L arranged in a mesh configuration between twelve leaf switches 154 and twelve spine switches 152, with each leaf switch 154 having a port connected to a port of each spine switch 152. The trunk cable 155 includes a trunk segment 157 within a jacket 157A, and first and second groups of tubes 156, 158 (also known as fanout tubes). The optical shuffle box 160 includes a housing 161 that contains ports 162A-162L and ports 164A-164L. Multiple optical fiber connections 163 are provided within the shuffle box 160. Use of the optical shuffle box 160 to connect with the spine switches 152 entails use of a small number of simple multi-fiber jumper cables relative to the much larger number of single-fiber connections that would be required in the absence of an optical shuffle box (as shown in FIG. 5), thereby enabling a well-organized fiber layout at a switch rack supporting the spine switches 152. Within an optical shuffle box 160, distances between the ports 162A-162L and ports 164A-164L are typically substantially less than one meter.
Utilization of an optical shuffle box adds two multifiber connections (e.g., through each pair of serially arranged ports 162A to 164A through 162L to 164L) for each link, which increases cost and also increases optical insertion loss. Additionally, the large number of connection points per link can subject the network system to a higher probability of failure due to dust contamination in the connectors. Optical shuffle boxes also entail significant cost and consume valuable space inside switch racks.
In view of the foregoing, need remains in the art for cable assemblies that address the above-described and other limitations associated with conventional shuffle box connectivity solutions (e.g., for leaf-spine networking in datacenters), as well as associated fabrication methods.